1. Field of the Invention
The invention relates to the field of airfield facilities and, in particular, to an airfield facility for docking and cargo handling system for lighter-than-air vehicles.
2. Description of Related Art
There are basically two types of lighter-than-air vehicles; rigid or non-rigid. There are three general types of non-rigid vehicles: those comprising a single gas filled bag; several gasbags joined together in series; and, of course, those having a multiple number gasbags within a non-rigid envelope. Rigid airships have an internal structure defining the shape of the vehicle and contain a plurality of gasbags therein and with an outer aerodynamic cover there over. In non-rigid designs the cargo flight station and cargo compartments are suspended from the bottom of the vehicle in what is most often referred to as a gondola. In rigid designs it is also common practice to mount the flight station/passenger and cargo compartments under the gasbag, although many designs integrate them in to the rigid frame of the vehicle.
One of the problems with both rigid and non-rigid lighter-than-air vehicles is their limited ability to station keep and/or maneuver when docking, especially if there are any significant cross-winds. This is due primarily to their large cross-sectional area that causes the vehicle to "weather vane" and "wave" with the wind. They are particularly difficult to control if the wind is gusting or when there are significant up or down drafts. In fact, docking has proven to be the most difficult portion of a flight for a lighter-than-air vehicle. Thus the most common docking procedure is moor the vehicle by its nose and let it weather vane.
Additionally, unlike a conventional aircraft, the lift force developed by the gasbag remains when docked. Thus as cargo is unloaded, the net lift force increases. In the past, this increase in the net lift has been absorbed by docking restraints, for example mooring lines. If the cargo weight is very large, the force exerted on the mooring lines becomes large and "station keeping" when docked becomes even more difficult. Therefore, unloading and reloading of cargo sometimes must wait until any winds have sufficiently died down or additional mooring lines must be used to "lock" the vehicle in one position. It is obvious, however, that it is always important to minimize the time spent in such operations.
The docking aspects of the problem was addressed in U.S. Pat. No. 1,119,646 "Device For Landing Or Berthing Airships" by H. V. Schleinitz wherein a rotating platform for docking lighter-than-air vehicles is disclosed. In addition, U.S. Pat. No. 1,867,591 "Dirigible Air Dock" by A. S. Pranke discloses a rail mounted rotating platform. U.S. Pat. No. 1,748,500 "Mooring Of Airships by" H. V. Thaden discloses the use of circular tracks having devices for supporting the vehicle such that the vehicle can align with the prevailing wind. U.S. Pat. No. 1,853,777 "Method Of And Apparatus For Berthing Airships" by W. V. N. Powelson, et al. discloses a rotatable suspension system for docking a lighter-than-air vehicle wherein the suspension system is rotated so that it is aligned with the relative wind. After the vehicle is secured the suspension system is rotated such that the vehicle is aligned with a below ground level pit that is used to shelter the vehicle. While all these concepts allow the vehicle to dock and to weather vane after docking; none of the above concepts provide for simultaneous loading and unloading of cargo, while the vehicle weather vanes.
The conventional loading of cargo containers and the like through doors located on the side of the vehicle is too slow and it would be difficult to simultaneously load and unload cargo in order to maintain the gross weight of the vehicle constant. Cargo aircraft, such as the C-5 military transport, have front and rear opening doors to the cargo compartment. However, moving the cargo simultaneously in the front and out the rear of a large lighter-than-air vehicle would still be a difficult and a time consuming operation, especially if the cargo compartment is some 600 to 800 feet long. In addition, requiring an uninterrupted passageway over such a length would greatly complicate the design of the gondola. The use of individual cargo compartments located along either side of the vehicle can reduce the cargo loading and unloading time, but does not address the need to maintain a constant payload weight on the vehicle.
The need to maintain a constant payload weight during loading and unloading of cargo and to provide a cargo loading system that minimizes the docking time for unloading and loading cargo was addressed by the invention disclosed in co-pending patent application Ser. No. 08/148,224, entitled "A Cargo Loading System For A Lighter-Than-Air Vehicle" by G. Belie, et al., filed Nov. 8, 1993. This invention is a cargo compartment for a lighter-than-air vehicle. In detail, the cargo compartment includes a cargo carrying structure mounted to the bottom of the vehicle having a plurality of passageways extending along the longitudinal axis of the vehicle. Each of the passageways is aligned with the lateral axis of the vehicle and extends completely through the structure and is adapted to provide simultaneous unloading of cargo from one end and loading of cargo from the opposite end. A cargo moving system is mounted in the floor of each passageway for moving the cargo in one end and out the opposite end of the passageway and to intermediate positions therebetween. A cargo securing system is mounted on the floor of the passageway for releasable securing the cargo within the passageway at the intermediate positions. Thus not only is a significant amount of time saved, but the weight of the vehicle remains essentially constant.
However, the problem of bringing the cargo to and from the vehicle when the vehicle weather vanes must be simultaneously addressed in order to insure that the time advantage of the above described cargo system is not lost. Besides the cargo issue, there is the problem of refueling of the vehicle, as well as conducting the necessary maintenance of the vehicle when it weather vanes.
U.S. Pat. No. 5,143,323 "Airship Handling System" by F. Husain discloses a rotating platform for docking a vehicle. The platform incorporates an arresting gear assembly. The cargo is contained in a module that is mounted in an open recess at the bottom of the vehicle. The module is removed at a first position on the platform and lowered down therein. The vehicle must be moved to a second position for the loading of a replacement module. This design has several drawbacks, among which are that the cargo can not be simultaneously loaded and unloaded, and the vehicle must be moved after unloading to a new position for reloading. These drawbacks greatly increase the turn-a-round time and complicate the design of the platform. Additionally the use of a cargo module in such a manner, requires that it be designed and certified as part of the vehicle airframe, greatly increasing its cost.
Thus it is a primary object of the subject invention to provide a docking system for a lighter-than-air vehicle.
It is another primary object of the subject invention to provide a docking system for a lighter-than-air vehicle that can accommodate the vehicle when it weather vanes during docking and after docking during cargo loading, refueling, maintenance and storage.
It is a further another object of the subject invention to provide a docking system for a lighter-than-air vehicle that is compatible with conventional cargo transporting systems.